Hydraulic cylinders are the most common actuator used on work vehicles to swing backhoe booms, raise and lower booms and dippers, articulate vehicles, raise buckets, tilt buckets, extend and retract stabilizers and a variety of other tasks.
Hydraulic cylinders are subject to extreme forces. The operating pressures in hydraulic cylinders can easily reach 1500 pounds per square inch. These pressures are large enough to permit the cylinders to move the devices to which they are coupled at great speed. Often, the speeds are great enough that the vehicle can be damaged over time. Further, the noise of impact can be excessive as the various component bang into each other.
Reaching a “stop” in this context means reaching the greatest possible extension or retraction of the cylinder itself, whether that extension or retraction is stop by structures within the cylinder, or structures to which the cylinder is coupled.
To reduce this potential damage, hydraulic cylinders have been coupled to mechanical and electrical devices that decelerate the cylinder reducing its speed of movement as the cylinder approaches one of its two stop positions. Mechanical devices include such things as self-contained hydraulic dampers or resilient shock absorbers that engage the cylinder (or more typically, a mechanical linkage coupled to the cylinder) in the last few centimeters of travel. The advantage to mechanical devices is that they are simple and robust.
Electrical devices have also been devised to decelerate the cylinder as it approaches a stop position. These systems typically include an electrical circuit coupled to a valve that controls the flow of hydraulic fluid to the cylinder. The circuit senses the position of the cylinder and throttles the flow of hydraulic fluid to the cylinder as the cylinder approaches a stop. One example of the circuit like this is shown in US patent application publication 2004/0045289 A1.
In the '289 reference, a controller 40 is coupled to a valve 35 which controls the flow of fluid to a cylinder 17. Controller 40 is also coupled to a sensor 20 that indicates the position of a swing angle of a working machine—in this case an excavator. When the operator swings the excavator boom, the sensor senses that the boom is approaching a limit of movement (i.e. approaching a stop). Controller 40 throttles the valve controlling fluid flow to cylinder 17. This reduction in flow decelerates the rate the cylinder extends or and slows the cylinder and excavator boom to a halt just as the boom and cylinder reach the stop.
Drawbacks of both the mechanical and electrical systems are that they cannot be easily and temporarily turned off—they always damp the movement of the hydraulic cylinder. The operator occasionally prefers to “bump” the implement against its stop, bringing the implement to a sudden halt. Such bumping is useful to empty an implement bucket having sticky material, or to shake dirt off the implement itself. If the hydraulic cylinder is only capable of smoothly decelerating a bucket without any sudden impact, the operator will never be able to empty the bucket or dislodge the earth.
What is needed, therefore, is an arrangement for turning off cylinder damping or cushioning in order to provide a sudden halt against a stop. What is also needed is a system for selectively permitting an implement to make sudden halt against a stop in one mode of operation and to make a gentle cushion stop in a second mode of operation. What is also needed is a system to select between these two modes of operation. What is further needed is a system for automatically selecting between these modes of operation requiring little if any operator intervention. What is also needed is a system for selecting one of these modes using the operator input device that also commands the movement of the cylinder. It is an object of this invention to provide such a system.